Much is known about how inputs from sources other than the retina affect the thalamic relay of retinal signals in route to the visual cortex. They arse from a variety of subcortical and cortical sources, comprise the bulk of synapses onto thalamic relay cells and act as modulators to affect the gain of retinogeniculate signal transmission. The superior collliculus (SC), a primary retino-recipient structure, also sends a prominent projection to the dorsal lateral geniculate nucleus (dLGN), the first order nucleus that conveys retinal signals to visual cortex. However, whether SC input acts as a driver to help shape the receptive field structure of dLGN relay neurons or as a modulator to dampen or amplify the flow of thalamic information remains untested. To understand how information arising from the SC influences dLGN function and how particular SC cell types contribute to this, we shall make use of mouse transgenics to visualize or target cell types and projections of the tectogeniculate pathway, optogenetics to photo-activate SC inputs to evoke postsynaptic activity in dLGN cells, and in vitro and in vivo recording techniques to assess whether SC inputs behave as drivers or modulators of dLGN activity. These combined approaches will allow us to selectively control the neuronal activity of the tecto-geniculate pathway and shed light on how interactions between two retino- recipient subcortical structures affect the processing and transfer of visual information. PUBLIC HEALTH RELEVANCE: These studies will provide valuable information about how first-order sensory nuclei of the thalamus receive and process information from peripheral sense organs. They shall also reveal how afferent input from central structures can modulate the flow of thalamic information in route to sensory cortical areas. Understanding the functional and structural organization of thalamic circuitry with optogenetic tools may offer further insight into the study and treatment of neurological disorders that result from the formation of abnormal patterns of connectivity.